Fixed-film biological treatment, wherein bacteria grow as slime or attached film on fixed surfaces, over which, or through which, the wastewater is circulated, has been a method of biological treatment for many years. For example, trickling filter wastewater treatment plants use fixed biological films, which were developed in the late 1800's using rock for the fixed surfaces. Fixed biological films are used routinely for cost effective treatment of both industrial and municipal wastewater streams.
The placement of fixed surfaces in trickling filters has involved the application of “structured sheet media” which is more efficient than the large rocks originally used in trickling filters. Structured sheet media is comprised of thin corrugated plastic sheets (PVC, polypropylene or other plastics) which are fastened together to form sizable blocks, which are typically one to two feet high, about two feet wide and about four feet long, with large surface areas that can be stacked in towers. Wastewater is trickled from the top of the tower of structured sheet media down through the media providing sustenance for the bacteria to grow. Air can also move vertically through the structured sheet media stack, since the stack is typically 95% void volume between the thin plastic formed sheets. The movement of air through the media provides an aerobic biological environment for treatment of the wastewater.
The same structured sheet media is also used when submerged in wastewater, commonly referred to as submerged fixed film (SFF), to accumulate, support and retain bacteria that can affect wastewater treatment in both aerated and un-aerated wastewater environments. The structured sheet media can also aid in the distribution of diffused air injected under the media.
An introduction of activated sludge wastewater treatment technology and submerged fixed-film biological treatment of wastewater has recently emerged in the wastewater treatment industry. The combination of these two technologies has given engineers a method of increasing the capacity of existing wastewater treatment plants for total nitrogen removal or for shrinking the foot print of new biological treatment systems. The integration has been named the IFAS process, IFAS being an acronym for Integrated Fixed-Film Activated Sludge.
Formed plastic structured sheet media is disclosed in U.S. Pat. No. 4,668,443, granted to Palle Rye on May 26, 1987, wherein the formed plastic sheets are arranged to form alternating apices in the parallel and generally vertical sheets. In U.S. Pat. No. 6,544,628, issued on Apr. 8, 2003, to Richard Aull, et al, the corrugated sheets, designed for cooling tower applications, are formed with projections that allow adjacent formed sheets to be coupled together, with the projections being inserted into a corresponding depression on the adjacent sheet and crimped to hold the two sheets together.
It would be desirable to improve the distribution of water in a trickling filter application where water is dispersed above the media and distributed throughout, but particularly laterally with respect to the orientation of the media, as the water moves down the media block. It would also be desirable to improve air distribution in submerged applications as the air rises through the media to enhance an air-lift pumping action and improve oxygen transfer efficiencies. It would be desirable to improve the air and/or water distribution through various applications, including trickling filter applications, submerged fixed film applications, integrated fixed film activated sludge applications, and cooling tower applications.